Outta curiosty how do i make Game play movies?
Three ways really.
1) One is to record demos (g_synchronousclients 1; record <filename>; stoprecord; g_synchronousclients 0). This is the primary method, although demos are only playable in-game (using the same patch version as the one recorded in and it causes some lag in game when doing so). Demos are only recordable in MP mode.
2) Next method is to use the avidemo console command, which makes it snap screenshots continually (until your hard drive fills up or you turn it off). Then you take those hundreds of screenshots and piece them together in a program like Adobe Premier to make a movie (but it will lack sound). This method is painstaking and takes a lot of disk space, but the benefit is that it works in SP mode.
3) The third and perhaps the best method is to use a program like FRAPS. This will capture a video of the action going on, with sound, etc. since it captures the action warts and all you can use it to get SP as well as MP. The only problem is that FRAPS is a shareware program and it only works on Windows 2000 and XP.
I don't record a lot of movies myself (I should though) so I can't give you all the specifics and tips, but that's basically the three methods to making a JA/JK2 movie.
Now, if you wanted to make In-game Cutscenes that's another matter entirely. Those require map-making and scripting skills, which you can look up on the editing forums.
Supposing I wanted to blend the two how would I do that?
You mean edit a video with screen grabs? Well take the movie you made and the screen caps and go into a video editing program like Premier and edit away.
You can't very well merge a demo into something else, since it's a thing only usable in JA.
Though I suppose you could record a demo, then later video record it, then edit the video to how you wanted (ie: turn your game playing into a music video or something).
There are forums and sites most likely covering this very thing, so do some searching...